Water concentration profile in silica glasses during surface crystallization

Water concentration profiles in silica glasses during surface crystallization at 1400°C in air were determined by IR spectroscopy with a microscope attachment. Three types of silica glasses with different water contents were examined. Some glass samples initially experienced hydration or dehydration depending upon the original water content. During crystallization, water concentration was highest at the crystal–glass interface and decreased with depth from the interface. Furthermore, water concentration at the interface increased with increasing heat-treatment time for crystallization. The observed water concentration profiles were consistent with the theoretical prediction by Smoluchowski based upon water diffusion modified by water expulsion from the crystal phase. A time-dependent crystal growth rate was also observed for some samples and this behavior appears related to the variation of water content in glasses.